1. Field of the Invention
The present invention relates to a molding apparatus and method for shaping a plastic or metal substance without producing undesirable burrs.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 160518/90 discloses a molding machine for encapsulating a circuit or other electronic parts in resin (see FIG. 9). A lead frame is sandwiched between upper and lower molds. The lower mold has a cavity for receiving an encapsulating material such as epoxy resin under pressure. A groove is defined around and spaced from the cavity to form a partition therebetween. A resilient gasket made of silicon rubber is fitted in the groove and projects slightly upwardly from the upper surface of the lower mold. When the upper and lower molds are clamped together, the gasket is elastically deformed to closely contact with the lead frame. However, the encapsulating resin still tends to leak from the mold cavity and enter between the lower surface of the lead frame and the partition. When this occurs, undesirable burrs will result. This is due to the fact that the lead frame is placed in metal-to-metal contact with the end surface of the partition, and a clearance of the order of a few microns remains between the lead frame and the partition. The resulting burrs not only physically damage the gasket, but also cause the molten resin to leak from the mold cavity. This molten resin could chemically damage the gasket and thus, reduce the service life of the gasket.